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I've been working on my B some and was just thinking about putting a 5.9 Cummins in it. That would make the truck much more practical to actually use some. Has anyone done this swap? I assume Mack used a standard SAE bellhousing a for the duplex behind the EN-402, so getting a Cummins SAE bellhousing wouldn't be a big deal. I'm not sure what to do for an air compressor though. What do y'all think about this?

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we have also tossed around the idea of a small cummins repower for a B42. the 401 has a #3 bellhousing I believe. air compressors are not really an issue. can always add abelt driven one. the only issue you might have is water pump shaft length. might have to cut the shaft off and use a hot rod style fan mounted to the radiator.

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That was my thoughts on it. I don't have the 402 running yet, but to hear everyone talk they are such slugs that it's not really worth the effort. It will be pointless to have the truck if I can't drive it without getting run over because it can't keep up with traffic.

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I swapped out the drive line in my B-42P , EN-402,Duplex and rear diff with all Mack components. It was a very easy swap as the frame was predrilled for either gas or diesel mounts. Everything was bolt in. I bought the front half of a B-61SX to get all the bits and pieces needed and found a good rebuilt END-673, Double over Tri-plex and a CRD-117 Differential with 4.64 ratio.. Ran the 673 for over 10 years until it ate an exhaust valve seat. Then upgraded to a 237, totally different truck with that engine.

If you have the Cummins that will save you, there will be a lot of fabricating though. You'll probably need to change out the differential as it will still be the original ratio. A double reduction diff will fit in a single reduction rear end. I think my original rear axle is a RAS-508 and it took the double reduction R-model diff without issue. Just some thoughts, good luck!!!

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I'm still waiting for the mack museum package, so I don't know what my ratios are in the rears or the trans. What are the high gear ratios in most of the duplex trans? The shift pattern placard call my trans a "10 speed overgear" I assume that means it's an overdrive unit. Do the triplexes and quads have higher high gear ratios or just lower on the low side and closer together?

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Two series of transmissions, 67 was the smaller gas jobs and the 72 series larger diesels. My original transmission was a TRD-67, direct duplex. A 0 added to the number,as in TRD-670, would be an overdrive and give you a .78 final drive out to the rear. Some transmissions are set up with an overdrive in each box, as in a TRT-720, which would give you a .68 final drive to the rear. There's a link here, I believe, that will take you to a site to break the numbers down and give you a ratio for each gear or someone will put it up. I can't recall where it is.

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B42's had Trd77's, not Trd67's. Mack used three different transmissions. the 77 they had 9, 10, 14, 18 and 20 speeds. the 67 series they only had 9 speed overgears,10 speed directs, and 10 speed overgears. you could get a B50 or B60 series wit either a 67 or a 72 but if you wanted a triplex or a quad you had to go with the 72 series. if you stick with a replacement engine that turns around 3000 rpm you can leave the rear end gears alone as long as you don't put something in there with too much torque for the transmission. I know its a bad word but I think an 8.2 litre Detroit would be a good swap and they were in tons of school busses over the years and might even have an air compressor.

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I am new to BMT and apologize in advance for any screw-ups. I have purchased a B42 Mack also and am in the same situation. My intentions were to pull a couple of antique tractors around, maybe my 5th wheel travel trailer. I am one for keeping everything original but converting it seems more logical. I also have the option to purchase a Blue Bird bus with a 5.9 cummins with an Allision trans. I was thinking of setting the body of the Mack on the bus frame and shorten the axle. that would give you the air, plus power steering, but not sure I could handle that much of a project at this time. There would have to be some revamping of the dropdown radiator and cooler. I have purchased the Mack B42 onsite, unseen except for a few pictures. The tag on the engine says magnadyne. I hope take delivered to my residence in Michigan before May.

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It might have been the 77 series, it was a while ago I did the swap. Regardless, it was the "baby duplex", not the larger series 72 that I put in later. There is an adapter plate used by Mack to put the smaller transmissions on the larger engines, making up the difference in bell housings. The important thing is do your research and find the components that will make it do what you want. An auto math book will be invaluable finding the right ratios for gearing using the right equations. The parts are out there to put almost anything in it to make it work for you and have a cool head turner.

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The B-61 donor for my truck was the key. The transmission mounts, front cross member, radiator, shutters and many miscellaneous small parts were all there. Using Mack components made it all so easy. Maintenance is also easy. The bonus for me was taking apart the donor and finding a power steering box in it, as i bought it originally for the transmission, which I never used.

Axles and springs were not a huge concern as I wasn't planning on hauling big weights, antique cars mostly, on a roll back body. The ride is good with my set up. Been all the way out to Colorado and all over the Northeast with it.

My current setup is a ENDT-675, TRTL-720 and a CRD-117 (4.62) final drive. Gives me 1600 RPM @ 65 MPH and 80 plus against the governor.

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